1. Field of the Invention
The present invention relates to a method and a device for removing bubbles in a liquid such as fluid used in hydraulic systems, lubrication oils coating solutions in paper-making machines, paints, chemical solutions such as ink, liquid foodstuffs, and so forth.
Applicable industrial field bubbles in a liquid of the kind described must be removed therefrom because they cause degradation of the fluids, poor product quality, increased compressivity, vibration of equipment and annoying noise.
2. Brief Description of the Related Art
Description of the prior art A bubble removing method has been made known in which the liquid is introduced into a cylindrical body tangentially and bubbles dispersed in the liquid are collected at the swirl center by means of a centrifugal force which makes the bubbles collect where the wall side pressure is higher compared with the center of swirl flow so that they can be removed easily (Japanese patent No. 1371889).
In FIGS. 4 and 5, an example of a device for practicing such a method is shown. A conical or cylindrical body 21, which is a vessel with an internal cylindrical space, is closed at its upward end by a lid 22. One or two inlet ports 23, in which liquid flows tangentially, are located on the cylindrical body close to the lid. Inlet port 23 is connected with a pump 28 through supply line 24. In the Figures, the other end of the cylindrical body 21 is closed by lid 26 where an outlet port 27 is open and is connected with a fluid discharge line 25.
With the above-mentioned structure, the liquid is introduced into the cylindrical body 21 tangentially by the pump 28 with some inflow velocity, and forms a swirl flow inside the body with centrifugal force acting upon the liquid. Consequently, the pressure at the center of the swirl becomes lower in comparison with that of the inner wall region of the body, and so bubbles concentrate towards the swirl center. The pressure at the center of the swirl flow is lowest in the vicinity of the inlet port 23 and increases as the liquid flows downstream; then pressure reaches maximal value and thereafter drops, and a gas column 30 is formed as indicated by lines at the center of the swirl in the vicinity of inlet port 23.
Because the swirl flow has the bubbles coalescing function, the pressure of the center of the cylindrical body in the vicinity of the inlet port 23 is lowered into negative pressure in general, if no pressure restriction is interposed in the downstream line of the cylindrical body, resulting in suction of air from the vent line 32 installed at the center of lid 22 located at the upward end of the cylindrical body 21. In order to solve the problem, a resistance means 29 interposed in the discharge line 25 is controlled so that the above-mentioned pressure of the center of the cylindrical body in the vicinity of inlet port 23 becomes higher than the atmospheric pressure plus liquid head. The resistance means is provided to produce comeback pressure, and vent valve 31 of vent line 32 is opened a little, and the collected bubbles are discharged through the vent line to the outside, and thus bubbles in fluid are eliminated.